Jeremy Corbyn was a hit when he addressed hundreds of people in Sparkbrook, Birmingham, over the weekend.

There were cheers when he told his audience: “We are living in an increasingly brutalised and unfair society. Labour must, can and I believe will be able to offer something different and something better.”

But the left-winger, who began the Labour leadership contest as an outsider but could end up winning, is not such a hit with Labour MPs.

He has supporters within the Parliamentary Labour Party, of course. But he couldn’t even obtain the 35 nominations needed to take part in the contest without help from MPs who don’t actually intend to vote for him.

And now that it looks like there’s a real chance of him winning, there is a concerted effort by some MPs to try to halt his progress - and concern that he won’t be able to command the support of his party in Parliament if he does get in.

What happens if he wins?

It remains to be seen whether the level of support in the Bordesley Centre, a Birmingham community hall, will be reflected in the result announced on September 12, once the votes are all counted.

Some opinion polls suggest he is in the lead. But the ballot is open to Labour members, registered supporters and members of affiliated organisations such as trade unions who choose to sign up as supporters, and there’s no list of their names and addresses available to the polling companies.

Mr Corbyn himself has pointed out that it’s hard to see how the polls can be based on reliable data.

It’s clear, however, that his opponents are taking him seriously.

"A generation in the wilderness"

Birmingham MP Jack Dromey, Labour MP for Erdington, wrote a piece in the New Statesman magazine designed to appeal to Labour activists attracted to Mr Corbyn’s left-wing stance of saying "no" to austerity and taking on the banks.

It’s not good enough to insist you have the right policies if the electorate disagrees and refused to elect you to government, Mr Dromey said. He warned: “It cannot be right that ever again we preside over decline, comfortable and preserving our credentials.”

Speaking to me, he said: “You cannot simply say that we are right and the electorate are wrong. That is a certain recipe for a generation in the wilderness.”

"End the madness"

Former Home Secretary Alan Johnson, who like Mr Dromey is backing Shadow Home Secretary Yvette Cooper’s campaign to become Labour leader, wrote an article urging Labour to “end the madness” over Mr Corbyn.

It’s not a coincidence that on the same day as these two politicians published articles, well-known Guardian columnist Polly Toynbee, also a supporter of Mrs Cooper, published a piece urging the party not to accept Corbyn.

These were deliberate interventions. But other MPs have also expressed concern about the prospect of Mr Corbyn winning.

"Difficult to command discipline"

Black Country MP Tom Watson (Lab West Bromwich East) warned Mr Corbyn could struggle to command the loyalty of Labour MPs because he had been so disloyal to leaders in the past.

He said: “It would certainly be a difficult thing for him to try and command discipline within parts of the Parliamentary Labour Party.”

Mr Watson, who is likely to become Labour’s next deputy leader, has not come out in support of any of the candidates for the leadership. This was not a deliberate attack on Mr Corbyn but simply his answer to a question on the subject during an interview with The Huffington Post.

Arguably, though, that does even more to highlight the real fear some Labour MPs have about what could happen to the party if Mr Corbyn wins.

"Greens, Tories and Communists voting in our election"

Birmingham MP Steve McCabe (Lab Selly Oak) has expressed concern about the way the leadership contest is being conducted. Anybody, more or less, can have a vote if they sign up as a “registered supporter” by noon on Wednesday August 12. It costs £3 and it’s as simple as sending a text message.

He said on Twitter: “I find it peculiar that people voting against Labour only 12 weeks ago are now electing our leader”, and suggested some of Mr Corbyn’s supporters may have voted “Green, Tory or any variant of Socialist/Communist just a few months ago”.

"Tories would love Labour to be led by Corbyn"

Black Country MP Ian Austin (Lab Dudley North) has warned “The Tories would love Labour to be led by Corbyn” and said he was “scared of what would become of us if he won”.

Pat McFadden, Labour MP for Wolverhampton South East, retweeted a comment from a journalist who stated: “Jeremy Corbyn’s candidacy has shown us who are the genuine left in UK and who are the fake left- and how thoroughly nasty the latter group are.”

So what happens if Mr Corbyn wins? Mr McCabe has said: “I’ll accept outcome of election and try to support whoever wins.”

No doubt many other Labour MPs will take the same approach.

But following May’s election defeat, a number of Labour MPs on the right of the party lamented that they had made a mistake in keeping quiet when they believed former leader Ed Miliband was taking the party in the wrong direction - and vowed not to make the same error again.